This invention relates to a composition of matter including UO.sub.2 F.sub.2 and an organic compound capable of interacting with the UO.sub.2 F.sub.2.
UO.sub.2 F.sub.2 is a powder material encountered in the production of UF.sub.6, which is subsequently used in isotope enrichment schemes for the production of enriched uranium oxides for use as a fuel in nuclear fission reactors.
UO.sub.2 F.sub.2 is also the product of hydrolysis of UF.sub.6 with water and in certain processing schemes, particularly the fluidized bed hydrolysis of UF.sub.6 with dry steam, is isolated and transported as a solid for subsequent reduction to UO.sub.2 to be used as a fuel for light water nuclear reactors.
UO.sub.2 F.sub.2 in powder form is difficult to handle and move in production situations due to the hygroscopic nature of the material and its propensity to cake. The present invention is a composition of matter including UO.sub.2 F.sub.2 which provides UO.sub.2 F.sub.2 in a form which eliminates these above stated problems providing a free flowing, non-hygroscopic powdery solid.
Uranyl fluoride prepared at low temperatures is very hygroscopic whereas that prepared at high temperatures exhibits no diliquescence even after extensive contact with air, see J. J. Katz and E. Robinowitch, NNES, VIII-5. The Chemistry of Uranium, Dover Publications, Inc. (1951). This property of uranyl fluoride is exemplified in the UF.sub.6 to UO.sub.2 conversion process as described by Knudson et al, see I. E. Knudsen, H. E. Hottman, and N. M. Levitz, ANL-6606 (1963). In this described process gaseous UF.sub.6 together with dry steam is injected into a fluidized bed of UO.sub.2 F.sub.2 seed particles to effect hydrolysis of the UF.sub.6 to UO.sub.2 F.sub.2. Even when this process was carried out at a reported 200.degree.-230.degree. C. (which is above the reported decomposition temperature of discrete uranyl fluoride hydrates, a problem was reportedly observed which consisted of the coating of the internal surfaces of the reaction apparatus and subsequent off-gas piping with a layer of UO.sub.2 F.sub.2 particles. While the rate was not considered excessive, it was estimated that shutdowns for cleaning and deplugging would be necessitated. While it was found that a higher reaction temperature (500.degree. C.) would reduce the caking and plugging problems encountered at lower temperatures, a problem of excessive fines formation resulted. Hence, it can be concluded that for the process to be used effectively a lower temperature must be employed and the product will then exhibit hygroscopic and deliquescent properties.
This is further substantiated in this same referenced report wherein a UO.sub.2 F.sub.2 product of a low temperature hydrolysis was found to absorb significant amounts of water from the atmosphere during storage in a closed container. Because of the reported hygroscopic and deliquescent tendencies of this low temperature product and the reported difficulty in freeing the UO.sub.2 F.sub.2 from residual water, it would appear some treatment would be desirable which would permit storage of low temperature preparations of UO.sub.2 F.sub.2 for long periods of time under ambient conditions without formation of troublesome hydrspecies.
These compositions because of their compositional stoichiometries and stabilities are useful for the storage, transportation and subsequent use of very precisely measured amounts of particular organic Lewis bases which may be required for various chemical reactions involving these Lewis bases.
In addition, these compositions may be included in a process for producing UO.sub.2 F.sub.2 if the compositions are produced from a reaction of a uranyl salt and a fluoride salt, see discussion below and copending Applns. Ser. No. 752,722 and Ser. No. 752,736 assigned to the same assignee as the present invention, which are incorporated herein by reference.
UO.sub.2 F.sub.2 exhibits high Lewis acidity and certain of its properties (high metal oxidation state and layered structure) suggest that compositions can be formed by it with molecular Lewis bases.
For example, stable compounds of uranyl fluoride with molecular Lewis bases can be formed by two possible mechanisms. (1) Normal coordination type compounds can be formed in which the Lewis base donates at least a pair of electrons to the central metal ion to form a coordinate covalent bond directly between the electron rich donor atom and the uranium ion. This type of material should exhibit, at equilibrium, an integral ratio of Lewis base to uranium moiety. (2) Because of the structure of UO.sub.2 F.sub.2, consisting of electrically neutral layers, stable intercalation compounds can be formed by simple insertion of the molecular Lewis base between the layers of the UO.sub.2 F.sub.2. In this situation, although at equilibrium the Lewis base should assume a definite position in the lattice in relation to the uranium ions, no interaction between the heteroatom(s) of the Lewis base and the uranium ion can be construed because of interatomic distance, geometry and steric interactions to be indicative of formation of discrete, directed chemical bonds. The thermodynamic stability of this type of material arises from van der Waal's interactions and the polarizabilities of the molecular Lewis base and/or the uranyl fluoride lattice. The Lewise base/uranium ratio in these types of compounds has the possibility of assuming either integral or non-integral values.
Lewis base intercalation compounds including metal chalcogenides have been disclosed in the prior art, see German Patent Application 2,061,162, Chalcogenide Inclusion Compounds, F. R. Gamble, et al.
Materials made from Lewis based interacting with UO.sub.2 F.sub.2 have been disclosed in the prior art. The composition UO.sub.2 F.sub.2 + NH.sub.3 was disclosed by A. von Unruh, dissertation, University of Rostock (1909) as reported by J. Katz and E. Rabinowitch, The Chemistry of Uranium, Dover Publications, Inc., New York, N.Y.
A composition [(UO.sub.2 F.sub.2).sub.6.(TBPO).sub.8 ], where TBPO = (C.sub.4 H.sub.9).sub.3 P = O, is a polymeric material soluble in benzene was disclosed in the papers by S. M. Sinitsyna and N. M. Sinitsyn, Dokl. Akad, Nauk SSSR 164(2), 851 (1965) and V. M. Vdovenko, A. I. Skoblo, D. N. Suglokov, L. L. Shcerbakova, and V. A. Shcherbakov, Russian Journal of Inorganic Chemistry 12(10) 1513 (1967).
In addition, a hydrate composition, UO.sub.2 F.sub.2.H.sub.2 O, was disclosed in the paper by A. A. Tsvetkov, V. P. Seleznev, B. N. Sudarikov and B. V. Gromov, Russian Journal of Inorganic Chemistry 17(7) 1048 (1972).
None of the compositions referenced above are suitable for the uses discussed above, namely, improvement in the handling characteristics of solid UO.sub.2 F.sub.2 without sacrificing chemical stability or the ability to provide precise delivery and metering of desired organic Lewis Bases.